Miniature, electric power drawing elements, such as integrated circuits, semiconductors and the like, included within a larger host device typically have many electrically conductive pads. Each conductive pad requires electrical contact with one or more corresponding conductive pads on the same element or associated elements of the host device to form an electrically conductive connection between the pads. The electrically conductive connection is provided by a segment of fine, electrically conductive wire which extends between the pads and is bonded to a bonding site on each of the pads. Wire bonding is an automated operation performed during assembly of the host device using a machine having a high degree of speed and precision. The wire bonding operation is cyclic, comprising many bonding cycles integrated into a continuous unitary process. Each bonding cycle of the process comprises a number of discrete tasks performed sequentially by specific components of the wire bonding machine.
In a simple case where an electrical connection is required between only two pads, the bonding cycle comprises the tasks of retaining an element or elements including the pad pair, feeding a wire from a wire supply to the pad pair, positioning the wire at the first bonding site on the first pad of the pair, bonding the wire to the first bonding site, repositioning the wire at the second bonding site on the second pad of the pair, bonding the wire to the second bonding site, and breaking off the wire at the second bonding site to provide a wire segment which electrically connects the first and second pads. These tasks are repeated in the next bonding cycle at another pad pair. For more complex bonding cycles where electrical connection is required between a string of three or more pads, the wire is positioned and bonded to the bonding site on each pad of the string in series. The wire is not broken off until the bond is completed at the final bonding site to provide a wire segment which electrically connects every pad of the string.
U.S. Pat. No. 4,610,387, incorporated herein by reference, discloses a device, commonly termed the "bond head", which is an assembly of cooperative components integrated into a wire bonding machine to perform the particular bonding cycle tasks of positioning the wire at a bonding site, bonding the wire to the bonding site, repeating the positioning and bonding tasks at the next bonding site and breaking off the wire at the final bonding site. It is apparent that each task in the bonding cycle has an associated time requirement. The present invention recognizes a need for a bond head which performs the tasks necessary to bond a wire to a plurality of bonding sites within a reduced time to render the wire bonding operation more time efficient, while satisfying the exacting performance requirements of the resulting bonds.
Therefore, it is an object of the present invention to provide an effective high-speed bond head. This object and others are accomplished in accordance with the invention described hereafter.